Apparatus for producing purs semiconductor material



Sept. 12,1967 A; KERSTING ABPARATUS FOR PRODUCING PURE SEMI ICONDUCTOR MATERIAL Filed July 21, 1965 United States Patent corporation of Germany Filed July 21, 1965, Ser. No. 473,789 Claims priority, applicationlGermany, July 21, 1964,

1 Claim. c1.11s-49.s

My invention relates to apparatus for the pyrolytic production of pure semiconductor material and constitutes an improvement over the apparatus described and illustrated in the copending application Ser. No. 168,756, now Patent No. 3,286,685 of Herbert Sandmann et al. and assigned to the assignee of the instant application.

Methods and apparatus for producing semiconductor material such as germanium and silicon are known wherein the semiconductor material is deposited by pyrolytic dissociation or chemical conversion from a gaseous compound of the semiconductor material, upon a heated carrier structure of the same semiconductor material. The semiconductor material is preferably deposited from a mixture of a gaseous compound of a semiconductor material and a carrier gas that is also capable of acting as a reaction partner such as a reducing agent for example. Hydrogen has been found to be particularly well-suited for this purpose. Gaseous compounds of semiconductor material that are applicable may be halogenides such as silicon tetrachloride or silicochloroform when the semiconductor material to be deposited is silicon, or corresponding germanium compounds when the semiconductor material to be deposited is germanium. The method and the apparatus for carrying out the method are known for example from US. Patent No. 3,011,877. The foregoing copending application and patent relate to apparatus for producing pure semiconductor material such as silicon for example by thermic dissociaton from substance in the gaseous or vaporous phase which contains in chemical combination a component material that is to be precipitated, the precipitation being effected upon an electrical structure or several such structures serving as current-traversed electric resistance conductors. A base plate is provided through which the electrical conductors, gas inlet tubes and gas outlet tubes as well as the carrier structures, upon which the semiconductor material is to be precipitated, extend. A bell-shaped receptacle is seated upon one of the surfaces of the base plate surrounding the conductors tubes and carriers structures extending therethrough.

Further in accordance with the apparatus of the aforementioned copending application, the base plate is made of metal and has a surface ground to planar shape facing the inner spaced defined by the bell-shaped receptacle. An auxiliary heat-shielding plate is placed on top of the base plate and in face-to-face contact therewith. The auxiliary plate and the bell-shaped receptacle consist of a material similar in thermal effect such as quartz, for example.

The apparatus of the copending application accordingly has the advantage that the space or chamber defined by the auxiliary plate and the bell-shaped receptacle and in which the thermic or pyrolytic conversion takes place is bounded on all sides by walls of the same material. Thus, high purity of deposited semiconductor material is thereby afforded. The surface of the auxiliary plate which faces the inner space of the bell-shaped receptacle is kept at an elevated temperature, whereas the base plate proper is not subjected to this elevated temperature. Consequently the auxiliary plate acts as a heat shield. The formation of oily polysilanes, which might lead to ex- "ice plosive phenomena when the receptacle is opened, is thereby avoided at the surface of the auxiliary plate that faces the inner space of the receptacle.

It is an object of my invention to provide apparatus that will increase the efficiency of production and preserve the very high purity of the semiconductor product even after prolonged periods of operation.

With the foregoing and other objects in view I provide apparatus of the type shown and described in the co ending application wherein the auxiliary plate has a polished surface on the side thereof facing the base plate and a rough surface at the side thereof facing the inner space of the receptacle.

Several advantages are derived from this improvement over the apparatus of the aforementioned copending application. Because the surface of the auxiliary plate facing the base plate has a polished surface, there is, therefore, no likelihood that reaction gas can penetrate from the interior chamber of the bell-shaped receptacle into any space intervening between the base plate and the auxiliary plate because the polished surface ensures the absence of virtually any space therebetween. The possibility that undesirable oily polysilanes will form in small quantities at the colder base plate is thus completely eliminated. In accordance with a further feature of my invention, the side of the base plate which faces the auxiliary plate is also polished so that therefore two polished surfaces rest upon one another with virtually no space therebetween.

At the surface of the auxiliary plate that faces the inner space of the bell-shaped receptacle, temperatures may rise locally which will cause the occurrence of a slight reaction at least locally of the reaction partners or reactants, and semiconductor material will consequently be precipitated from the vapor or gaseous medium. If the surface of the auxiliary plate facing the inner space of the bell-shaped receptacle is rough or irregular, as in r the invention of this application, the material forming near the auxiliary plate is precipitated on this rough surface. It grows there relatively firmly and cannot cause any disruption in the carrying out of the method or in the operation of the apparatus. When the surface of the auxiliary plate facing the receptacle chamber is not rough, it is possible that the material deposited thereon will peel off and whirl about within the chamber due to the movement of the gas current supplied thereto. Particles of this whirling material can then also deposit on the precipitation carrier structures where they will act as secondary seeds and will greatly disturb the desired uniform growth of semiconductor material thereon. It is particularly in the production of monocrystalline semiconductor material, for which purpose the precipitation carrier structures have been previously formed as monocrystalline semiconductor rods, that the secondary seeds would have a very disturbing elfect since they can prevent monocrystalline growth altogether.

Other features which are considered as characteristic for the invention are set forth in the appended claim.

Although the invention is illustrated and described herein as embodied in apparatus for producing pure semiconductor material, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claim.

The construction of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following de scription of a specific embodiment when read in connection with the accompanying single figure of the drawings which shows a vertical section through the apparatus.

As shown in the figure, the apparatus comprises a base plate 2, traversed by a flow of coolant through a suitably provided coolant flow system having an inlet 3 and an outlet 4. A receptacle 6 having a bell-shape for forming an enclosed processing space is provided with a flange at its lower edge by means of which the bell 6 is seated on the top surface of the base plate 2 with a gasket ring 5 inserted between the flange and the base plate 2. Though not illustrated, suitable clamping devices such as a plurality of C-clarnps can be employed for clamping the bell flange and the base plate 2 together. Two precipitation carrier structures 7, 8 consisting of semiconductor rods are located inside the bell-shaped receptacle 6 and may consist of monocrystalline silicon for example having a length of approximately 20-30 cm. and a diameter of 5 or 6 mm. The two semiconductor rods 7 and 8 are connected to one another at their upper ends by a bridge-like connecting piece 9 Which can either consist of semiconductor material also or of pure graphite. At their lower ends the two rods 7 and 8 are mounted in two holders 10 and 11 which can also be formed of pure graphite. The holders 10 and 11 simultaneously serve as input and output leads for the electric current required to heat the rods 7 and 8. For this purpose, at least one of the two holders i.e. the holder 11 as shown in the drawing, is insulated with respect to the base plate 2, for example by means of the insulation 12. The other current-conducting holder 10 in the illustrated embodiment extends uninsulated through the base plate 2 and is connected with the grounded pole of a current source 13 which may be the source either of direct current or alternating current. A variable resistor 14 as shown in the drawing is meant to symbolize means in general for regulating the amount of the supplied current with respect to the growth rate of the semiconductor material and can of course be comprised of any other suitable components or combination of components for effecting such regulation. Thus an increased current supply is provided for a greater rod thickness if the precipitation temperature of the precipitation carrier structures 7 and 8 is to be mainv tained at the same value.

A pipe line 15 additionally extends through the base plate 2 for supplying reaction gas mixture to the interior of the precipitation receptacle 6. The pipe line 15 is formed with a nozzle-shaped end 16 located within the reaction chamber. An exhaust pipe line 18 is also provided for discharging the predominantly exhausted gas from the reaction chamber. As viewed in the drawing, the exhaustgas pipe line 18 is located on the opposite side of the plane of the drawing from that of the inlet gas pipe line 15. An auxiliary plate 17 overlying the base plate 2 is also provided. The auxiliary plate 17 is lapped completely to planar shape at the surface thereof facing the base plate 2 and is thereafter polished. The surface of the plate 17 facing the inner space of the receptacle 6 however, has a rough and irregular shape which can be produced by sandblasting if necessary or by suitable chemical treatment. The bell-shaped receptacle 6, the nozzle 16 and the auxiliary plate 17 all consist of quartz glass. Thus, virtually all of the surface exposed to the gas mixture inside the receptacle 6 consists either of quartz glass, pure graphite or semiconductor material.

I claim:

In apparatus for producing pure semiconductor material by thermal dissociation and precipitation of the material, from a gaseous substance that contains the material as a component, onto precipitation carrier structure electrically heated by being traversed by electric current, and comprising a processing vessel having a base of metal with a ground planar top surface and a bell-shaped receptacle gas tightly sealed on the top surface to provide an enclosed processing chamber, the base having duct means for supply and discharge of processing gas to and from the chamber, electrically conductive holder means mounted on the base in the chamber for holding and electricall energizing the precipitation carrier structure, the receptacle consisting of material different from that of the base, and an auxiliary plate removably seated on the top surface of the base in face-to-face contact therewith and extending substantially over the entire inner cross-section of the receptacle adjacent to the top surface, the auxiliary plate having substantially the same thermal properties as the receptacle and formed with. openings through which the holder means protrude and openings for the duct means, the improvement which comprises providing the auxiliary plate with a polished surface at the side thereof abutting the base plate and a rough surface at the side thereof facing the processing chamber and providing the base plate with a polished surface abutting said polished surface of the auxiliary plate.

References Cited UNITED STATES PATENTS 3,009,841 11/1961 Faust 148179 X 3,014,791 12/1961 Benzing et a1. 23--223.5 X 3,232,800 2/1966 Mihara et a1 148179 3,235,418 2/1966 Nickl et al 148174 3,286,685 11/1966 Sandmann et al 11849.1 3,293,074 12/1966 Nickl 1l7106 MORRIS KAPLAN, Primary Examiner. 

